"Type 1 diabetes is more dangerous for women than men, study finds,” The Daily Telegraph reports. A large review found gender inequality in overall deaths among people with type 1 diabetes, and also deaths due to heart disease...

"Type 1 diabetes is more dangerous for women than men, study finds,” The Daily Telegraph reports. A large review found gender inequality in overall deaths among people with type 1 diabetes, and also deaths due to heart disease.

These results come from a systematic review of studies looking at how risk of death in men and women with type 1 diabetes differs from their counterparts without the disease. It pooled results from 26 studies, and found that type 1 diabetes was associated with a greater increase in risk of death from any cause, or death from heart disease, over a given period in women than it is in men.

The researchers suggest it may be because diabetes is less well controlled among girls and women than among boys and men. If this proves to be the case, then greater efforts may be targeted towards to improving diabetes management in women.

Where did the story come from?

The study was carried out by researchers from the Universities of Queensland and other universities in Australia, the Netherlands, UK and US. The researchers were funded by a Niels Stensen Fellowship, an Australian National Health and Medical Research Council Fellowship, and an Australian Research Council Future Fellowship. The study was published in the peer-reviewed medical journal The Lancet.

The Daily Telegraph covers this study reasonably well; however, the results are expressed in a way that could be misleading. It says, for example, that “female patients are twice as likely to die from heart disease than men with [type 1 diabetes]”. It is not quite as simple as this. As men do not generally live as long as women, researchers needed to take this into account in their analyses – otherwise, the figures would not be showing them the potential impact of diabetes, but the effect of gender.

So, to get a fair idea of the potential impact of diabetes, the researchers did not directly compare rates of death in men and women. Instead, they first compared the risk of death over a given period in women with type 1 diabetes to that of women in the general population, to see what effect diabetes had in women. The equivalent comparison was then made for men.

These figures were then compared to see whether type 1 diabetes had a greater or lesser effect on risk of death in women than in men.

What kind of research was this?

This was a systematic review that aimed to determine whether there was any difference between men and women with type 1 diabetes and their likelihood of dying within any given period.

The researchers say that although management of type 1 diabetes has improved, the condition is still associated with an increased risk of death over a given period, compared to the general population. They say that some studies have suggested that men and women may differ in how much type 1 diabetes affects their risk of death, but no review has ever pooled the results of these studies.

A systematic review is the best way to identify and summarise the best-quality studies available to answer a given question. This review statistically pooled (meta-analysed) the results of the studies it identified. The meta-analysis includes more people than each individual study alone, and this means it is better able to detect differences between groups, if they exist.

What did the research involve?

The researchers systematically searched one major research literature database (PubMed) to identify studies that identified risk of death in men and women with diabetes over time. They selected those studies which had data that would allow them to compare the effect of type 1 diabetes in terms of risk in men and women. They then extracted and pooled the results of these studies to see if there was a difference overall.

The researchers only included studies that provided information on deaths in a form that they could use. This meant either hazard ratios (HR), comparing deaths among people with and without type 1 diabetes, or standardised mortality ratios (SMR), comparing deaths among people with type 1 diabetes against what would be expected among people with similar characteristics in the general population.

As men and women have different expected lifespans, researchers were looking for studies which compared deaths among women with type 1 diabetes versus women without the disease, and did the same for men. This meant they could compare the likelihood of a person of each gender dying to someone of the same gender without the disease. They then compared these figures.

The researchers were mainly interested in deaths from any cause, but also looked at deaths from specific causes separately. They also looked at new diagnoses of various conditions, including coronary heart disease (where a build-up of fatty substances causes blockage in the arteries providing blood to the heart muscle) and cardiovascular disease (coronary heart disease, stroke, or other cardiovascular disease). They also looked at various factors which might affect the outcome, such as how long the studies followed people for, or the quality of the study.

The researchers complied with accepted standards for pooling of this study type and for reporting their systematic review.

What were the basic results?

The researchers identified 26 studies that provided the data they wanted. These studies included 214,114 people, although not all of them were included in all of the analyses.

It found that during follow up, women with type 1 diabetes were 5.8 times more likely to die than women in the general population, and men with type 1 diabetes were 3.8 times more likely to die than men in the general population. Overall this equated to a 37% greater relative increase in likelihood of death than men with the condition (ratio of SMRs for women versus men: 1.37, 95% confidence interval [CI] 1.21 to 1.56). There was statistical evidence that different studies in this analysis had varying results. Some of this variability seemed to be due to differences between the studies in exactly how likely men and women were to die.

Women with type 1 diabetes also had a greater relative increase than men with the condition in terms of risk of:

There was no difference between men and women in how type 1 diabetes affected their risk of cancer or accident and suicide.

How did the researchers interpret the results?

Researchers concluded that “women with type 1 diabetes have a roughly 40% greater excess risk of all-cause mortality, and twice the excess risk of fatal and nonfatal vascular events, compared with men with type 1 diabetes”. They say that greater understanding of this issue “is likely to have profound clinical implications for how women with type 1 diabetes are treated and managed throughout their life course”.

Conclusion

This systematic review suggests that type 1 diabetes is associated with a greater increase in risk of death in women than men.

A systematic review is the best way to identify and summarise the best-quality studies available to answer a given question. The pooling (meta-analysis) of the studies' results means the review includes more people than the individual studies, and is therefore better able to detect differences between groups.

The figures presented are comparisons of the relative increases in risk of death associated with type 1 diabetes within each gender. As women generally live longer than men, even though the relative increase in risk in women with type 1 diabetes may be greater than in men, the women’s actual (absolute) risks of death in a given period may not differ as much, and could still be less than men’s risks.

There are some other limitations and points to note:

This study is only about type 1 diabetes, so results may not apply to those with type 2 diabetes.

The review only searched one literature database, and also looked for relevant studies mentioned in the studies they identified. Ideally, systematic reviews search more than one literature database to increase their chances of finding all relevant studies.

The pooled studies did have differences in their designs and methods, and this may influence the results. There was statistical evidence that there were differences in the results of the individual studies, which the researchers were not entirely able to explain. In part, it related to different risks of death in the populations being studied. This may mean that the pooled results are not representative of each different study population. The researchers also say it means their results “remain speculative until confirmed by future studies”.

The review pooled observational studies. Factors other than type 1 diabetes (confounders) could be influencing the results seen. The individual studies differed in the extent to which they took these factors into account, so they could still be having an effect. The researchers think that this is unlikely to be a big issue, as the same confounders should be affecting men and women, and therefore effectively cancelling each other out.

It is likely that more research will go into exploring why this difference might exist. The researchers suggest it may be because girls’ and women’s diabetes is less well controlled, or due to hormonal differences. The researchers were not able to look at diabetes control in men and women in the included studies to see if there was a difference. If the difference does prove to be due to poorer diabetes control, then greater efforts could be targeted towards improving diabetes management in women.

Whatever the reason for these findings, they do not take away from the fact that good diabetes control is important for both genders, to maintain a person’s health and reduce the risk of complications from the disease.